Say no to rubbish (6)
I believe the answer is:
refuse
This clue is a double definition.
'say no' is the first definition.
(I've seen this before)
'rubbish' is the second definition.
(both can mean waste material)
'to' acts as a link.
(Other definitions for refuse that I've seen before include "Decline, repudiate" , "Deny; rubbish" , "Say no to - waste" , "Say no to - rubbish" , "'Deny, turn down (6)'" .)